I bought an XSI about 2 years ago, and I am finding I can't do everything I want with it. Specifically I have started to notice the noise even at an ISO at 100, and I would really like to be able to do long exposure night shots to get the trailing star effect.

I have been looking at the T2i, but I don't know if it is a wise move. Is the overall image quality going to be better, and will I be able to do the long exposures for night shots? If not what camera would you suggest? I want to stick with Canon so I can re-use my lenses. I also want to be able to do time lapse photos. My XSI can only take a dozen (I think.) Is the T2i going to be able to do more?

I want to keep it under $1K, but if there is a much better advantage to going over a bit I am open to it.

The improvement in quality you seek may just be turning on Long Exposure Noise Reduction, or changing to shooting in RAW and using DPP or other software to remove the noise from the photos (I find the DPP software very good and simple).
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DreamagerAug 16 '11 at 13:41

I already shoot in raw, but ill give the LENR a try
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JoeAug 16 '11 at 17:20

Owning the XSi myself, and having a couple friends who own the T1i and T2i, I can state that there is definitely an improvement in image quality going from the XSi to the T2i. The technology is several years improved on the T2i, as the XSi uses much older sensor tech and more basic image processing chips. The XSi does not perform well at all when moving beyond ISO 400, and ISO 1600 is practically unusable for low-light photography. It only really performs decently when you have enough light to use a lower ISO anyway. In contrast, the T2i performs quite well at ISO 1600, and does decently well at ISO 3200.

My friends and I do quite a bit of night sky photography, and there is no question that for short-exposure night sky photography of the milky way and constellations, the T2i does FAR better than the XSi. My camera (the XSi) is unusable at ISO 1600, but ok at ISO 800. Even with a wide 50mm f/1.4 lens, its pretty tough to get a decent milky way shot with the XSi. With the T2i, getting good milky way shots is much easier as ISO 1600 is perfectly usable, and longer shots, up to 25-30 seconds, are a breeze. For star trails, there isn't much of a difference, as you use a low ISO and stop down the aperture a bit anyway, but the T2i offers quite a bit more resolution, so its still a win.

I do a lot of moon photography (partly because I love the moon, and partly because the moon is the only thing visible when I have time to do any photography these days -_- ). The XSi fares decently, however its limited dynamic range does pose a problem at times. The T2i is a tad bit better in the area of dynamic range, although not a whole lot.

Regardless of the kind of long exposure photography you hope to do, night sky photography is an excellent test. Comparing the XSi with the T2i for night sky photography, the T2i is definitely an improvement.

Awesome, I'm glad you have been able to compare them side by side. Would you say the upgrade is worth it, or should I save my pennies and go straight to the 7D?
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JoeAug 16 '11 at 5:12

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Joe, jrista gave an excellent, first hand experience answer, but only you can decide if 7D is more worthy than the T2i, or if any of them worth the upgrade from XSi. This is really your personal decision.
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ysapAug 16 '11 at 8:13

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@Joe: Well, both upgrades are worth it, really. Its just a difference of degree. The 7D is obviously a stellar camera, being part of Canon's official professional grades, and definitely better than the T2i. The price difference is almost $1000 more for the 7D, and thats only something you can decide if its worth it.
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jrista♦Aug 16 '11 at 15:51

My guess is that the short answer is - probably yes, you get improved long exposure performance on the full image. I deduce it from the higher maximum ISO of the newer camera. That said, smaller pixels are noisier at the pixel level, so it is possible that you will not see improvement when pixel-peeping.

To answer you question in the comments: the dpreview side-by-side comparison suggests that you will definitely see a gain from the change. The question is if the difference justifies buying a new camera. You will get higher resolution, more speed, better AF, (much) better LCD, higher max ISO, wider EC range. Do you feel limited by the XSi w.r.t these parameters? Above all these - do you need video capability? If so, then T2i wins easily.

@Joe in total score, but if you look at it stat by stat, the clear winner is the 7D - by a clear margin. Their total score system is just flawed.
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rfuscaAug 15 '11 at 21:38

@Joe - the comparison page you linked to clearly shows that the 7D is preferable over the T2i. The reasons you should choose a T2i are (1) size [note that once I moved from Rebel XT to 7D, I can't go back. The small size is a disadvantage for me] (2) price. In any other aspect, I don't see why one would choose the T2i.
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ysapAug 15 '11 at 21:45

So I wont see any good gains going from the xsi to the t2i?
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JoeAug 15 '11 at 21:49